Closure systems are known which comprise a stopper in the form of a tubular body closed by an end disk which is placed over the neck of a bottle or flask that needs to be closed.
The closure is usually sealed by means of a sealing disk which is placed against an end wall of the stopper and which is compressed between the end wall of the stopper and the annular end of the bottle neck when the bottle is closed.
One of the oldest techniques consists in screwing the stopper onto the neck. In this case, the degree to which the sealing disk is compressed depends on the force exerted by the user each time the stopper is screwed onto the bottle neck. However, it has been observed that some users, in an effort to ensure proper sealing, tend to screw on the stopper too tight, thereby crushing the sealing disk and rapidly leading to its destruction.
In more recent techniques, the closed position corresponds to a relative position of the stopper and the neck which is theoretically well determined. This is the case when the stopper is fixed to the neck of the bottle by means of internally projecting lugs on the inside surface of the stopper engaging steeply sloping ramps or cam surfaces on the outside of the neck with end stops present to ensure that the stopper comes to rest in a predetermined angular relationship with the neck. This kind of system is essential if the stopper and the bottle neck are not of circular symmetry, eg. if they are of polygonal cross section for the sake of appearance or styling.
With respect to sealing, this technique theoretically has the advantage that the degree to which the sealing disk is compressed is independent of the force exerted by the user when the bottle closing. However, in practice, if the bottle is made of glass, conventional glass making techniques do not lend themselves, unfortunately, to small tolerances, in particular in the axial direction, between different portions of the neck of the bottle. There are thus considerable variations in the degree of sealing from one bottle to the next, due to the sealing disk being compressed by differing amounts.
Published French patent specification No. 2 471 926 proposes to solve this problem by providing a system in which the degree of sealing obtained in the closed position is independent of the relative axial position of the neck of the bottle and of the stopper. This system includes a flexible cylindrical skirt projecting from the end wall of the stopper into the bottle neck and coming into contact with the inside surface of the bottle neck.
However, it is not always easy to provide such a cylindrical skirt inside the stopper, in particular when the stopper is intended to fit small bottles or flasks.